1. Technical Field of the Invention
The present invention relates to an impingement cooled structure that cools hot walls of a turbine shroud and a turbine end wall.
2. Description of the Related Art
In recent years, in order to improve thermal efficiency, an increase in the temperature of a gas turbine has been promoted. In this case, the turbine inlet temperature reaches about 1200° C. to 1700° C. Under such high temperatures, metal turbine components need to be cooled so as not to exceed the service temperature limit of the materials thereof.
An example of such turbine components includes a turbine shroud 31 shown in FIG. 1. As shown in a cross-sectional view of FIG. 2, a plurality of turbine shrouds 31 are connected to each other in a circumferential direction to form a ring shape and surround fast-rotating turbine blades 32 such that the ring shape is spaced from the tip surfaces of the turbine blades 32. With this structure, the turbine shrouds 31 have a function of controlling the flow rate of hot gas flowing through a gap between the shrouds 31 and the blades 32.
Hence, the inner surfaces of the turbine shrouds 31 are always exposed to hot gas. Likewise, the inner surface of a turbine end wall is also exposed to hot gas.
In FIG. 2, the reference numeral 33 indicates a fixing portion, such as an inner surface of an engine, which allows the turbine shrouds 31 to be fixed thereto. The reference numeral 34 indicates fixing hardware.
In order to cool hot walls of the aforementioned turbine shrouds and turbine end wall, for example, as shown in FIGS. 3A and 3B, a conventionally employed cooled structure has impingement cooling holes 35, turbulence promoters 36 (or a smoothing flow path with fins), film cooling holes 37, or combination thereof.
However, cooling air used in such a cooled structure is usually high pressure air compressed by a compressor. Accordingly, there is a problem that the amount of the used cooling air directly affects engine performance.
In view of this, in order to reduce the amount of used cooling air, there is proposed a configuration in which cooling air which is once used for impingement cooling is used again for impingement cooling (e.g., Patent Documents 1 and 2).
[Patent Document 1]    Specification of U.S. Pat. No. 4,526,226, “MULTIPLE-IMPINGEMENT COOLED STRUCTURE”
[Patent Document 2]    Specification of U.S. Pat. No. 6,779,597, “MULTIPLE IMPINGEMENT COOLED STRUCTURE”
As shown in FIG. 4, an impingement cooled structure of Patent Document 1 includes: a shroud 47 having an inner surface 38, an outer surface 40, edges 42 and 44, and a rib 46; flanges 48 and 50; a first baffle 56; a second baffle 58; and fluid communication means. An upstream side of the outer surface 40 of the shroud 47 is cooled by impingement by means of cooling air which flows in the through holes of the first baffle 56. Furthermore, the same cooling air flows in the through holes of the second baffle 58 so as to cool the downstream side of the outer surface 40 of the shroud 47 by impingement.
As shown in FIG. 5, an impingement cooled structure of Patent Document 2 includes: a base 62 having an inner surface 64 and an outer surface 66; a first baffle 70; a cavity 72; and a second baffle 74. A downstream side of the outer surface 66 of the base 62 is cooled by impingement by means of cooling air which flows in the through holes of the first baffle 70. Furthermore, the same cooling air flows in the through holes of the second baffle 74 so as to cool the upstream side of the outer surface of the base 62 by impingement.
The impingement cooled structures of Patent Documents 1 and 2, however, need to have a plurality of air chambers (cavities) which are stacked in the radial outward direction on top of each other, and thus, have a problem of an overall thickness greater than that of conventional shrouds. In addition, these impingement cooled structures are complex as compared with shrouds prior to Patent Documents 1 and 2, causing a problem of an increase in manufacturing cost.